The NHS Covid-19 app has told 1.7 million people in England and Wales to self-isolate to date.
Health ministers have also revealed they believe it has prevented about 600,000 cases of the disease.
In a further disclosure, internal data indicates that about 16.5 million people are currently actively using its contact-tracing tool.
That figure is 24% below the app's latest download tally, which is the government's preferred measure.
The discrepancy is likely to be down to people uninstalling the app, turning off its contact-tracing capabilities, or simply failing to have activated it in the first place.
Each handset actively taking part sends a digital "heartbeat" once a day to the Amazon computer server involved, allowing the current usage figure to be calculated.
And while the number of total downloads has slowly grown from 20.2 million to 21.7 million over the past two months, the number of phones pinging the server has been more or less flat.